The invention relates to a method of inspecting surfaces of members for defects.
Members such as motor car body panels which are produced in large numbers may include some members or panels with defects. With steel body panels local defects such as surface pitting can occur but also on pressing of the panels, some may be manufactured with a defective shape.
In a finished motor car the most prominent way in which defects show up is in irregular distortion of reflections from a high-gloss finish. Regular distortion is of course to be expected due to the curvature of a panel.
It has already been proposed in the LORIA (Trade Mark) surface analyser system of Ashland Chemicals to analyse or inspect the surface of a panel by reflecting a laser beam from a panel onto a screen at a high angle of incidence to give a low angle of deflection (that is a small deflection from the incident direction) in the beam, scanning the beam across the panel to form a trace, recording the image of the trace on the screen, similarly producing traces, images and records for successive parts of the panel, and analysing the records of the images to give a measure of the shape and surface quality of the panel. The present invention is concerned with an improvement to a system of this kind.
The known system can be effective for detecting some surfaces with small degrees of curvature and small irregularities but some kinds of contour of the panel can not be detected effectively and accurately.
An objective of the present invention is to provide an improved system in which the above disadvantages are reduced or overcome.